Medication discrepancies, defined as unintentional differences found between patients' medical records and patients' reports of the medication they are taking, occur frequently after hospital discharge, predisposing to adverse drug events (ADEs), emergency department visits and readmissions. Resolving medication discrepancies - medication reconciliation - is mandated at every care transition, but little is known about intervention strategies to improve medication reconciliation in the post-discharge period, when patients may lack prompt access to primary care and are at high risk for ADEs. To address this gap, we developed and pilot tested the Secure Messaging for Medication Reconciliation Tool (SMMRT), with a pharmacist communicating with Veterans to review medications and reconcile discrepancies after hospital discharge via Secure Messaging (SM), within My HealtheVet (MHV), VA's patient portal. Our pilot study detected, on average, two clinically important medication discrepancies per Veteran immediately following discharge and demonstrated that Veterans could interact with the pharmacist asynchronously to resolve discrepancies. Veterans found SMMRT easy to use and indicated they would willingly use it again. We therefore propose the SMMRT Trial, in which we will optimize the end-users' experience with SMMRT, conduct a randomized controlled trial (RCT) of MHV training and SMMRT to reduce hospital utilization, and evaluate SMMRT for potential future implementation. For Aim 1, we will conduct formal usability assessment of SMMRT among Veterans (N=10) pharmacists (N=10) and nurses (N=10), refining the user interface for optimal acceptability and effectiveness. For Aim 2, we will mount a 3-arm RCT to evaluate the effects of MHV training and SMMRT, randomizing 1,400 hospitalized Veterans to compare 1) Usual Care (UC), 2) UC + MHV enrollment and training (i.e., MHV training), and 3) UC + MHV training + SMMRT after discharge. The primary outcome measure will be 30-day hospital utilization (combined readmissions plus emergency department visits) with the primary hypothesis that SMMRT will reduce hospital utilization compared with UC. For Aim 3, we will carry out a formative evaluation of the interventions for potential future implementation, with qualitative analysis of in-depth interviews from among 20 Veterans and 10-15 primary care nurses. We will collaborate with operational partners: the Veterans' Consumer Health Information Office, which oversees MHV program activities, and the National Medication Reconciliation Initiative, within Pharmacy Benefits Management, responsible for implementing the VA Directive regarding medication reconciliation. If proven effective, SMMRT will have several impacts on Veterans and their health care: 1) decreased medication discrepancies; 2) decreased emergency room visits and hospital readmissions following discharge, which are commonly the result of ADE; 3) improved measures of patient- engagement, patient-centeredness, and patient satisfaction. This study directly supports VA's Transformational Initiative to employ state-of-the-art information technology in the delivery of Veterans' health care.